Semiconductor device and method for producing the same

ABSTRACT

In a semiconductor device, circuit boards are connected electrically to each other by via-conductors that penetrate sheet members, semiconductor elements arranged between substrates are contained in element-containing portions formed on the sheet members, and a low-elastic material whose elastic modulus is lower than the elastic modulus of the thermosetting resin composition of the sheet members is filled in the space between the semiconductor elements contained in the element-containing portions and the substrates opposing surfaces opposite to the mounting surfaces of the semiconductor elements. Thereby, a semiconductor device resistant to warping and deformation and having a high mounting reliability is provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device used in anelectric/electronic apparatus, and a method for producing the same.

2. Description of Related Art

Due to an accelerated tendency toward miniaturization of portableelectronic apparatuses, there is a keen demand for downsizing andhigh-density mounting of electronic parts to be incorporated. Amongvarious electronic parts, semiconductor devices having multi-stagedstructures of laminating circuit boards including semiconductor elementshave been proposed particularly.

For an example of such semiconductor devices having multi-stagedstructures, JP H10-135267A proposes a semiconductor device includingcircuit boards that are electrically connected to each other with solderballs.

However, since such a semiconductor device is formed by laminating aplurality of packaged circuit boards, the overall thickness of thesemiconductor device will be increased. Moreover, when the connectionpitch is set to be 0.5 mm or less for the purpose of downsizing thesemiconductor device, a short circuit may occur between solder balls.Furthermore, since the circuit boards are required to be flat andparallel to each other for solder connection, there are considerablelimitations on the stiffness and thickness of the circuit boards.

For high-density mounting and reduction in thickness of thesemiconductor device, JP2003-218273A proposes, for example, asemiconductor device that is formed by alternately laminating, throughadhesive layers, circuit boards on which semiconductor elements aremounted and interlayer members having cavities for containing thesemiconductor elements, and embedding the semiconductor elements in thecavities by heat press. In the semiconductor device, the circuit boardsare electrically connected to each other through via-conductors formedin the interlayer members.

JP2002-261449A proposes a member-containing module with built-incomponents. The module contains semiconductor elements within a corelayer as an electrical insulating layer for the purpose of realizingdownsizing and reduction in thickness of electronic parts andimprovement of the functions.

For reducing thickness of a laminated semiconductor device, both thethickness of the semiconductor elements and substrates on which thesemiconductor elements are mounted must be reduced. Recently, thethickness of a substrate for mounting a semiconductor is reducedfurther; particularly, the thickness for a double-sided circuit board isreduced to 0.1 mm or less, and for a four-layered circuit board, 0.2 mmor less. According to the above-mentioned JP2003-218273A, asemiconductor element mounted on a resin substrate is embedded in acavity. However, since the cavity is formed in the vicinity of thesemiconductor element, the stiffness of the circuit board willdeteriorate when a thin resin substrate is used, and thus warping ordeformation may occur easily. Therefore, according to theabove-mentioned configuration, mounting reliability of the semiconductorelement and mounting reliability of the semiconductor device withrespect to a mother board may deteriorate.

According to the above-mentioned JP2002-261449A, the semiconductorelement is embedded entirely in a core layer. This configuration isexcellent in that heat dissipation of the built-in semiconductor elementwill be improved and deformation of the entire apparatus is unlikely tooccur, so the flatness will be improved. However, since thesemiconductor element is in a built-in state in the core layer, thermalstress occurring at the joint between the semiconductor element and thesubstrate will be increased, and thus mounting reliability in a heatcycle test or a reflow test after moisture absorption will deteriorateconsiderably. When the core layer is made of a low-elastic material forrelieving the thermal stress, the strength of the core layer willdeteriorate so that warping and deformation may occur easily.

SUMMARY OF THE INVENTION

Therefore, with the foregoing in mind, it is an object of the presentinvention to provide a semiconductor device that is unlikely to causewarping and deformation and has high mounting reliability, and a methodfor producing the same.

A first semiconductor device of the present invention is a semiconductordevice having a plurality of circuit boards including substrates andsemiconductor elements mounted on the substrates, the circuit boardsbeing bonded to each other through sheet members of a thermosettingresin composition, wherein

the plural circuit boards are connected electrically to each other byvia-conductors penetrating the sheet members,

the semiconductor elements arranged between the substrates are containedin element-containing portions formed in the sheet members, and

a low-elastic material whose elastic modulus is lower than the elasticmodulus of the thermosetting resin composition is filled in the spacebetween each of the semiconductor elements contained in each of theelement-containing portions and the substrate opposing the surfaceopposite to the mounting surface of the semiconductor element.

A second semiconductor device of the present invention is asemiconductor device having a plurality of circuit boards includingsubstrates and semiconductor elements mounted on the substrates, thecircuit boards being bonded to each other through sheet members of athermosetting resin composition, wherein

the plural circuit boards are connected electrically to each other byvia-conductors penetrating the sheet members,

the semiconductor elements arranged between the substrates are containedin an element-containing portion formed on the sheet member,

at least one of the semiconductor elements to be contained in theelement-containing portion is mounted on each of the two substratescovering the element-containing portion,

at least one pair of the semiconductor elements are contained facingeach other in the element-containing portion, and

a low-elastic material whose elastic modulus is lower than the elasticmodulus of the thermosetting resin composition is filled in the spacebetween surfaces of the pair of the semiconductor elements opposite tothe mounting surfaces.

A method for producing a semiconductor device according to the presentinvention includes the steps of:

mounting semiconductor elements on substrates so as to form circuitboards,

forming element-containing portions for containing the semiconductorelements and through holes to be filled with a conductor on sheetmembers of an uncured thermosetting resin composition,

filling a conductor in the through holes,

positioning the circuit boards and the sheet members and laminatingalternately, and applying heat and pressure while injecting alow-elastic material into the element-containing portions, where theelastic modulus of the low-elastic material is lower than the elasticmodulus of the thermosetting resin composition, thereby simultaneouslycuring the thermosetting resin composition and the low-elastic materialso as to incorporate, and electrically connecting the plural circuitboards.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a semiconductor deviceaccording to Embodiment 1 of the present invention.

FIGS. 2A-2H are cross-sectional views for showing process steps forproducing a semiconductor device according to Embodiment 1 of thepresent invention.

FIG. 3 is a cross-sectional view showing a semiconductor deviceaccording to Embodiment 2 of the present invention.

FIGS. 4A-4F are cross-sectional views for showing process steps forproducing a semiconductor device according to Embodiment 2 of thepresent invention.

FIG. 5 is a cross-sectional view showing a semiconductor deviceaccording to Embodiment 3 of the present invention.

FIGS. 6A and 6B are cross-sectional views for showing process steps forproducing a semiconductor device according to Embodiment 3 of thepresent invention.

FIG. 7 is a cross-sectional view showing a semiconductor deviceaccording to Embodiment 4 of the present invention.

FIG. 8 is a cross-sectional view showing a semiconductor deviceaccording to Embodiment 5 of the present invention.

FIGS. 9A-9D are cross-sectional views for showing process steps forproducing a semiconductor device according to Embodiment 5 of thepresent invention.

FIG. 10 is a cross-sectional view showing a semiconductor deviceaccording to Embodiment 6 of the present invention.

FIG. 11 is a cross-sectional view showing a semiconductor deviceaccording to Embodiment 7 of the present invention.

FIG. 12 is a cross-sectional view showing a semiconductor deviceaccording to Embodiment 8 of the present invention.

FIGS. 13A-13D are cross-sectional views for showing process steps forproducing a semiconductor device according to Embodiment 8 of thepresent invention.

FIG. 14 is a cross-sectional view showing a semiconductor deviceaccording to Embodiment 9 of the present invention.

FIG. 15 is a cross-sectional view showing a semiconductor deviceaccording to Embodiment 10 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A first semiconductor device of the present invention has a plurality ofcircuit boards including substrates and semiconductor elements mountedon the substrates, where the circuit boards are bonded to each otherthrough sheet members of a thermosetting resin composition. The circuitboards are connected electrically to each other with via-conductorspenetrating the sheet members, and the semiconductor elements arrangedbetween the substrates are contained in element-containing portionsformed on the sheet members. The thermosetting resin compositionincludes at least a thermosetting resin such as epoxy resin. For thevia-conductor, an inner via that allows a high-density mounting is usedpreferably. Alternatively, a penetration conductor formed by plating canbe used.

In the first semiconductor device of the present invention, alow-elastic material whose elastic modulus is lower than the elasticmodulus of the thermosetting resin composition is filled in the spacebetween a semiconductor element contained in an element-containingportion and the substrate opposing a surface (hereinafter, this may bereferred to as ‘upper surface’) opposite to the mounting surface of thesemiconductor element. Here, the term “a mounting surface of asemiconductor element” denotes either the upper or lower main surface ofthe semiconductor element, which faces the substrate on which thesemiconductor element is mounted.

In the first semiconductor device, the via-conductors are held by thesheet members of the thermosetting resin composition, and a low-elasticmaterial whose elastic modulus is lower than the elastic modulus of thethermosetting resin composition is filled in the space between thesemiconductor elements and the substrates opposing upper surfaces of thesemiconductor elements. Therefore, warping and deformation will beunlikely to occur even when thin substrates or thin semiconductorelements are used. Moreover, since the low-elastic material serves todecrease the thermal stress applied to the space between thesemiconductor elements and the substrates, the mounting reliability canbe improved. Furthermore, since the low-elastic material serves todissipate quickly heat generated at the semiconductor elements to theoutside. In this specification, the term “elastic modulus” denotes areserved elastic modulus at 25° C., and it can be measured by a methodcorresponding to JIS K7244. The elastic modulus of the low-elasticmaterial is lower, for example, by at least 1000 MPa in comparison withthe elastic modulus of the thermosetting resin composition.

In the first semiconductor device of the present invention, thesemiconductor elements contained in the element-containing portions canbe sealed with the low-elastic material in order to prevent degradationof the semiconductor elements.

In the first semiconductor device of the present invention, the cavitiesin the element-containing portions can be filled with the low-elasticmaterial in order to prevent deformation caused by the presence of thecavities, thereby providing a semiconductor device having a highmounting reliability.

In the first semiconductor device of the present invention, at least oneof the semiconductor elements to be contained in an element-containingportion can be mounted on each of two substrates for covering theelement-containing portion. Accordingly, a plurality of semiconductorelements can be contained in an element-containing portion so as toreduce thickness of the semiconductor device.

It is preferable in the first semiconductor device of the presentinvention that at least one of the semiconductor elements is flip-chipmounted on the substrate. According to this configuration, a reductionin thickness and high-density mounting of the semiconductor elements canbe performed easily.

Next, a second semiconductor device of the present invention will bedescribed below. Components identical to those of the above-mentionedfirst semiconductor device may be omitted from the followingdescription.

The second semiconductor device of the present invention has a pluralityof circuit boards including substrates and semiconductor elementsmounted on the substrates, and the circuit boards are bonded to eachother through sheet members of a thermosetting resin composition. Thecircuit boards are connected electrically to each other withvia-conductors penetrating the sheet members, and the semiconductorelements between the substrates are contained in the element-containingportions formed on the sheet members.

In the second semiconductor device of the present invention, at leastone of the semiconductor elements to be contained in theelement-containing portion is mounted on each of two substrates forcovering an element-containing portion, where at least one pair of thesemiconductor elements are contained facing each other in theelement-containing portion, and a low-elastic material whose elasticmodulus is lower than the elastic modulus of the thermosetting resincomposition is used to fill the space the pair of the semiconductorelements.

In the second semiconductor device of the present invention, the sheetmembers of the thermosetting resin composition hold the via-conductors,and at the same time, a low-elastic material whose elastic modulus islower than the elastic modulus of the thermosetting resin composition isused to fill the space between the pair of the semiconductor elements.Therefore, even when a thin substrate or a thin semiconductor element isused, warping and deformation rarely occurs, and the mountingreliability will be improved. Furthermore, since at least one pair ofsemiconductor elements are contained facing each other in theelement-containing portion, the surface area of the semiconductor devicecan be reduced easily.

In the second semiconductor device of the present invention, thecavities in the element-containing portion can be filled with thelow-elastic material. Accordingly, deformation caused by the cavity canbe prevented, and furthermore, thermal stress that will be applied tothe space between the semiconductor element and the substrate by thelow-elastic material can be decreased, and thereby the mountingreliability will be improved further. Furthermore, the low-elasticmaterial serves to dissipate heat generated at the semiconductorelements to the outside quickly.

It is preferable in each of the above-mentioned semiconductor devicesthat a moisture-absorbing filler is mixed in the low-elastic material inorder to prevent degradation caused by moisture of the semiconductordevice.

It is preferable in each of the above-mentioned semiconductor devicesthat thermo-conductive filler is mixed in the low-elastic material inorder to dissipate heat generated at the semiconductor elements to theoutside more efficiently.

It is preferable in each of the above-mentioned semiconductor devicesthat the elastic modulus of the low-elastic material is 1 to 1000 MPa,and more preferably, 50 to 500 MPa. An elastic modulus higher than 1000MPa is not so different from the elastic modulus of the thermosettingresin composition, and the above-mentioned effect of decreasing thethermal stress may not be obtained. When the elastic modulus is lowerthan 1 MPa, the above-mentioned effect of decreasing thermal stress canbe obtained, but warping and deformation may occur.

In a preferred embodiment for each of the semiconductor devices, thethermosetting resin composition contains an inorganic filler in anamount of 70 to 95 mass %. In this case, the coefficient of linearexpansion of the thermosetting resin composition gets closer to that ofthe via-conductors, and thus the connection reliability of thevia-conductors is improved. Moreover, the thermal conductivity of thethermosetting resin composition becomes higher, and thereby heatgenerated at the semiconductor elements can be dissipated efficiently.

In a preferred embodiment for each of the semiconductor devices, thethermosetting resin composition contains a reinforcer in an amount of 15to 50 mass %. In this case, warping and deformation in the sheet memberof the thermosetting resin composition can be prevented efficiently.

A method for producing a semiconductor device of the present inventionincludes: forming circuit boards by mounting semiconductor elements onsubstrates, forming element-containing portions for containing thesemiconductor elements on sheet members made of an uncured thermosettingresin composition and through holes to be filled later with a conductor.After positioning the circuit boards and the sheet members andlaminating alternately, the laminate is subjected to heat and pressurewhile a low-elastic material whose elastic modulus is lower than theelastic modulus of the thermosetting resin composition is injected intothe element-containing portions so as to cure and integratesimultaneously the thermosetting resin composition and the low-elasticmaterial, and at the same time, the plurality of circuit boards areconnected electrically to each other. Thereby, the above-mentionedsemiconductor device can be formed easily.

It is preferable in the method for producing a semiconductor device ofthe present invention that through holes are formed in the circuitboards, specifically in the vicinity of the areas for mounting thesemiconductor elements, before laminating the circuit boards and thesheet members, and the low-elastic material is injected into theelement-containing portions from the through holes. In this manner, thelow-elastic material can be injected into the element-containingportions with certainty.

Hereinafter, the present invention will be described by way ofillustrative embodiments with reference to the drawings. It should benoted that in the description of the embodiments, similar parts aregiven similar symbols, and duplicate description may be omitted.

EMBODIMENT 1

FIG. 1 is a cross-sectional view showing a semiconductor deviceaccording to Embodiment 1 of the present invention. As shown in FIG. 1,a semiconductor device according to Embodiment 1 has three circuitboards 12 including substrates 10 and semiconductor elements 11 mountedon the substrates 10, and these three circuit boards 12 are bonded toeach other through sheet members 13 made of a thermosetting resincomposition. The three circuit boards 12 are connected electrically withvia-conductors 14 penetrating the sheet members 13, and thesemiconductor elements 11 arranged between the substrates 10 arecontained in element-containing portions 15. In FIG. 1, 16 denotes awire, 17 denotes an electrode, 18 denotes a die-bond agent, 19 denotesan underfill, 20 denotes an element-mounting electrode, 21 denotes anexternal connection electrode, and 27 denotes a gold bump.

There is no particular limitation for the semiconductor elements 11, butsemiconductor elements made of, for example, Si, GaAs, GaAlAs, SiGe orthe like can be used. For the substrates 10, for example, multi-layeredceramic substrates comprising alumina and glass-alumina, and resinsubstrates comprising glass-epoxy, aramid-epoxy and the like, can beused. In light of the need for reduction of weight and cost, a resinsubstrate is preferred.

It is preferable that the thickness of the semiconductor element 11 isnot more than 100 μm. It is also preferable that the thickness of thesubstrate 10 is not more than 200 μm, and more preferably, not more than100 μm, so that the thickness of the semiconductor device can bedecreased easily.

For the main component of the thermosetting resin composition, athermosetting resin such as epoxy resin, phenol resin, modifiedpolyimide resin, polyamideimide resin, isocyanate resin and the like canbe used. These resins have excellent durability due to the excellentheat resistance.

It is further preferable that the above-mentioned thermosetting resincomposition contains an inorganic filler. Since the coefficient oflinear expansion of the thermosetting resin composition can be loweredby adding such an inorganic filler, the dimensional change caused by theapplication of thermal stress can be decreased. For the inorganicfiller, for example, a filler made of Al₂O₃, SiO₂, SiC, AlN, BN, MgO orSi₃N₄ is used preferably. Particularly, when an inorganic filler made ofAl₂O₃, SiO₂, SiC or AlN is used, the thermal conductivity of thethermosetting resin composition is improved, and heat dissipation fromthe semiconductor elements is increased. Two or more kinds of inorganicfillers can be mixed in use. For the inorganic filler, particles havinga diameter of 0.1 to 100 μm can be used preferably. It is preferablethat the thermosetting resin composition is a mixture of an inorganicfiller of 70 to 95 mass %, and a thermosetting resin of 5 to 30 mass %.When the content of the thermosetting resin is less than 70 mass %, thethermal conductivity of the thermosetting resin will not rise incomparison with a case of using the thermosetting resin alone, and thedissipation effect may not be obtained. When the content of theinorganic filler exceeds 95 mass %, mixing of the inorganic filler willbe difficult, and the electric insulation of the sheet members 13 candeteriorate.

It is preferable that the above-mentioned thermosetting resincomposition includes a reinforcer. A reinforcer included in thethermosetting resin composition can serve to prevent the via-conductorsfrom flowing to cause connection failure of the via-conductors duringlamination-integration in the below-mentioned process step of producinga semiconductor device. For the reinforcer, for example, a glass cloth,a glass nonwoven fabric, an aramid nonwoven fabric, an aramid film, aceramic nonwoven fabric or the like can be used.

The thermosetting resin composition can include further an additive suchas a curing agent, a curing catalyst, a coupling agent, a surfactant,and a coloring agent.

For the via-conductors 14, for example, a mixture containing at least aconductive powder and a thermosetting resin can be used. For theconductive powder, for example, a powder of a metal based on Ag, Cu, Au,Ni, Pd or Pt, or an alloy of these metals can be used. Particularly, apowder of Ag or Cu, or a powder of alloy containing Ag or Cu is usedpreferably. For the thermosetting resin, for example, epoxy resin,phenol resin, isocyanate resin, polyamide resin, and polyamideimideresin can be used. These resins can be used preferably because of theirexcellent durability.

A material for the underfill 19 can be selected suitably correspondingto the semiconductor mounting method. For example, a mixture based on athermosetting resin and a silica filler can be used. For example, theunderfill 19 has an elastic modulus of about 0.5 to about 15 GPa. Theelement-mounting electrode 20 is used suitably as required forextracting signals from the semiconductor elements 11, and an electrodemade of gold or the like can be used for this purpose.

The size of the element-containing portions 15 can be determinedsuitably corresponding to the size of the semiconductor elements 11 tobe contained. For example, space between a semiconductor element 11 anda substrate 10 can be in a range of 30 μm to 200 μm, and space betweenthe semiconductor element 11 and a sheet member 13 can be in a range of50 μm to 2 mm.

For the wire 16, for example, a metal wire of gold or aluminum can beused. Connection of semiconductors with the wire 16 can be carried outby using an ordinary wire bonder. For the material of the electrode 17,for example, aluminum, and alloy of aluminum and copper can be used. Forthe die-bond agent 18, a commonly available die-bond agent can be used.

In the semiconductor device according to Embodiment 1, a low-elasticmaterial 22 whose elastic modulus is lower than that of thethermosetting resin composition is filled in the space between asemiconductor element 11 contained in an element-containing portion 15and the substrate 10 opposing the upper surface 11 a of thesemiconductor element 11. Thereby, even when a substrate 10 having athickness of not more than 60 μm or a semiconductor element 11 having athickness of not more than 100 μm is used, warping and deformation willbe unlikely to occur. Moreover, since the thermal stress applied to thespace between the upper surface 11 a of the semiconductor element 11 andthe substrate 10 can be decreased, the mounting reliability will beimproved. Furthermore, the low-elastic material 22 serves to dissipateheat generated at the semiconductor element 11 to the outside quickly.In the semiconductor device according to Embodiment 1, the respectivesemiconductor elements 11 are sealed with the low-elastic material 22.Thereby, degradation of the respective semiconductor elements 11 can beprevented. The method for sealing the semiconductor elements 11 with thelow-elastic material 22 is not limited particularly, but potting or amethod of using a dispenser can be used for this purpose. At this time,it is preferable that the low-elastic material 22 is cured, and thecuring method can be selected from, for example, thermosetting,ultraviolet curing, and curing by moisture absorption.

For the low-elastic material 22, materials that have relatively highheat resistance can be used, and the examples include silicone resin,silicone rubber, urethane rubber, fluorine rubber, silicone gel and amixture of any of the materials and a thermosetting resin. Among them,silicone resin and silicone gel are preferred from a viewpoint of theheat resistance.

It is preferable that a moisture-absorbing filler is added to thelow-elastic material 22. By adding a moisture-absorbing filler, moistureentering from the exterior can be captured, and thus the connectionreliability with respect to the semiconductor element connection portionor the via-conductor connection portion can be improved. An example ofthe moisture-absorbing filler that can be used here will have 100 massparts when kept untreated for 72 hours under an atmosphere of 25° C. anda humidity of 30%. The filler will have 110 mass parts when keptuntreated for 72 hours under an atmosphere of 25° C. and a humidity of85%. Specific examples of the moisture-absorbing filler include silicagel, zeolite, potassium titanate, sepiolite and the like. The content ofthe moisture-absorbing filler in the low-elastic material is, forexample, in a range of about 20 to about 60 mass %.

It is preferable that a thermo-conductive filler is added to thelow-elastic material 22. Since the thermal conductivity of thelow-elastic material 22 can be improved by adding the thermo-conductivefiller, heat generated at the semiconductor elements can be dissipatedto the outside quickly. For the thermo-conductive filler, for example,Al₂O₃, BN, MgO, AlN, and SiO₂ can be used. The content of thethermo-conductive filler in the low-elastic material is, for example, ina range of about 30 to about 70 mass %.

In the semiconductor device according to Embodiment 1, a semiconductorelement 11 is flip-chip mounted on the upper surface of a bottomsubstrate 10 at the element-containing portion 15 side, while theremaining semiconductor elements 11 are mounted on the remainingsubstrates 10 by wire-bonding. Further, an external connection electrode21 is provided on the bottom substrate 10, specifically, on a surfaceopposite to the element-containing portion 15 side. Thereby, asemiconductor element 11 having a number of electrodes is flip-chipmounted on the bottom substrate 10 so as to improve the mountingefficiency. Furthermore, by wire-bond mounting another semiconductorelement 11 having a relatively small number of electrodes on anothersubstrate 10, the cost for producing the semiconductor device can bedecreased. In addition, since a semiconductor element 11 having a smallnumber of connection points is arranged on the top, the number of landscan be decreased, and thereby the surface area of the semiconductordevice can be reduced easily. An example of such a semiconductor deviceis formed by combining a logic semiconductor element typically having anumber of electrodes and a memory semiconductor element having arelatively small number of electrodes.

Next, a method for producing the above-mentioned semiconductor deviceaccording to Embodiment 1 will be described. FIGS. 2A-2H arecross-sectional views showing process steps in a method for producing asemiconductor device according to Embodiment 1. As shown in FIG. 2A, asemiconductor element 11 is bonded to a substrate 10 with a die-bondagent 18, and furthermore, an electrode 17 on the semiconductor element11 and an element-mounting electrode 20 are connected to each other witha wire 16 so as to manufacture a circuit board 12.

Subsequently, the semiconductor element 11 is sealed with a low-elasticmaterial 22 as shown in FIG. 2B, thereby manufacturing a semiconductorpackage 26.

Next, a sheet member 13 of an uncured thermosetting resin composition isprepared as shown in FIG. 2C. As shown in FIG. 2D, an element-containingportion (cavity) 15 is formed in the sheet member 13, and furthermore,through holes 28 are formed as shown in FIG. 2E. Subsequently, aconductor 29 is filled in the through holes 28 as shown in FIG. 2F.

The sheet member 13 as shown in FIG. 2C can be formed by any suitablemethod selected in accordance with the viscosity of the thermosettingresin composition in use. Specific examples of applicable methodsinclude a doctor-blade method, an extrusion method, a method of using acurtain coater, a method of using a roller coater, and a method ofimpregnating an uncured thermosetting resin composition in a reinforcer.A doctor-blade method or an extrusion method is used particularlypreferably due to the convenience. A solvent can be added to thethermosetting resin composition for adjusting the viscosity as required.Examples of the solvent used for the viscosity adjustment includemethylethylketone (MEK), isopropanol, toluene and the like. In a case ofadding these solvents, it is preferable that the thermosetting resincomposition is shaped into a sheet and subsequently dried to remove thesolvent ingredients. The method of drying is not limited particularly aslong as the temperature is set lower than the temperature at which thethermosetting resin composition starts curing.

The element-containing portion 15 can be formed by punching with a mold,a laser processor or a punching machine, for example. The through holes28 can be formed by punching with a carbon dioxide gas laser or apunching machine, for example. The diameter of the through holes 28 canbe selected suitably in accordance with the thickness or the like of thesheet member 13, and preferably it is not more than 300 μm, and morepreferably, not more than 150 μm. According to this preferred example,the mounting density can be improved remarkably in comparison with amethod of connecting circuit boards by using solder balls.

For the conductor 29 to form the via-conductors 14 (see FIG. 1), forexample, a mixed paste including a conductive powder and an uncuredthermosetting resin can be used. Examples of paste-mixing methodsinclude, for example, a three-roll method, a method of using a planetarymixer and the like. At this time, for example, 30 to 150 volume parts ofthe thermosetting resin composition are mixed with respect to 100 volumeparts of the conductive powder. Furthermore, a curing agent, a curingcatalyst, a lubricant, a coupling agent, a surfactant, a retarderthinner, a reactive diluent or the like can be added to the conductor29.

The method of filling the conductor 29 in the through holes 28 is notlimited particularly, and a screen printing method or the like can beused, for example.

The element-containing portion 15 and the through holes 28 as shown inFIGS. 2D and 2E can be formed simultaneously. The order of the processsteps shown in FIG. 2C to FIG. 2F can be exchanged. For example, thethrough holes 28 are formed and then the conductor 29 is filled in thethrough holes 28, and subsequently the element-containing portion 15 isformed.

Next, as shown in FIG. 2G, a plurality of semiconductor packages 26 anda plurality of sheet members 13 containing the conductor 29 arelaminated alternately. As shown in FIG. 2H, the components areintegrated with each other by applying heat and pressure, and the pluralcircuit boards 12 are connected electrically to each other with thevia-conductors 14 made of the conductor 29 so as to obtain asemiconductor device according to Embodiment 1. In the semiconductorpackage 26 positioned at the bottom in FIG. 2G, the semiconductorelement 11 is flip-chip mounted through a gold bump 27. An underfill 19is arranged between the flip-chip mounted semiconductor element 11 andthe substrate 10. The method of flip-chip mounting the semiconductorelement 11 is not limited particularly, but a well-known flip-chipconnection technique can be used. The method of arranging the underfill19 is not limited particularly, and the examples include a method ofthermocompression-bonding a sheet-like underfill 19 at a desiredposition on the substrate 10, and a method of mounting the semiconductorelement 11 on the substrate 10 and then injecting a liquid underfill 19from space between the substrate 10 and the semiconductor element 11.

The method of applying heat and pressure is not limited particularly,and examples thereof include a method of using a heat press with a mold,and a method of using an autoclave. The temperature and pressure can bedetermined suitably in accordance with the thermosetting resincomposition and the thermosetting resin in the conductor 29 in use, andin general, the temperature is in a range of 140 to 230° C. and thepressure is in a range of 0.3 to 5 MPa.

In FIG. 2G, a sheet member 13 containing a conductor 29 is arrangedbetween a pair of semiconductor packages 26. Alternatively, a pluralityof sheet members 13 can be arranged between a pair of semiconductorpackages 26. This method is preferred from a viewpoint that, since adistance between the semiconductor packages 26 can be changed withoutchanging the thickness of the sheet members 13, via-conductors 14 with ahigh aspect ratio can be formed easily.

EMBODIMENT 2

FIG. 3 is a cross-sectional view showing a semiconductor deviceaccording to Embodiment 2 of the present invention. As shown in FIG. 3,in a semiconductor device according to Embodiment 2, all of thesemiconductor elements 11 are flip-chip mounted. In the top andintermediate substrates 10 in FIG. 3, through holes 24 for communicatingwith element-containing portions 15 are formed, and penetrationconductor 25 for electrically connecting the wirings formed on both thesurfaces of the substrates 10 is formed on the through holes 24. Alow-elastic material 22 is filled in the cavities in theelement-containing portions 15. Namely, the semiconductor deviceaccording to Embodiment 2 has no cavities in the interior. Exceptingthis, the semiconductor device in this embodiment is similar to thesemiconductor device (see FIG. 1) according to the above-mentionedEmbodiment 1.

Since the above-mentioned through holes 24 are formed in thesemiconductor device according to Embodiment 2, the low-elastic material22 can be injected from the through holes 24 in the below-mentionedmethod for producing a semiconductor device. Thereby, it is possible tofill the cavities in the element-containing portions 15 reliably withthe low-elastic material 22. Moreover, since the penetration conductor25 is contained, the mounting density can be increased further.

Next, a method for producing a semiconductor device according toEmbodiment 2 of the present invention will be described. FIGS. 4A-4F arecross-sectional views showing process steps in a method for producing asemiconductor device according to Embodiment 2. As shown in FIG. 4A, asemiconductor element 11 is flip-chip mounted on a substrate 10 so as tosandwich an underfill 19 arranged on the substrate 10, thereby a circuitboard 12 as shown in FIG. 4B is manufactured. Through holes 24 areformed previously in the substrate 10, and provided with penetrationconductors 25. The method for forming the through holes 24 is notlimited particularly, and a method similar to the method of forming theabove-mentioned through holes 28 (see FIG. 2E) can be used, for example.Similarly, the penetration conductor 25 can be formed by a known platingmethod or the like, without any particular limitations.

Next, as shown in FIG. 4C, a plurality of circuit boards 12 and aplurality of sheet members 13 both formed in the same manner as shown inFIGS. 2C to 2F and having a conductor 29 are laminated alternately.These components are integrated with each other by application of heatand pressure as shown in FIG. 4D, and at the same time, a plurality ofcircuit boards 12 are connected electrically to each other withvia-conductors 14 made of the conductor 29. Neither through holes 24 norpenetration conductors 25 are formed in a circuit board 12 positioned atthe bottom in FIG. 4C.

The method of applying heat and pressure is not limited particularly,and the examples include a method of using a heat press with a mold, anda method of using an autoclave. The temperature and pressure can bedetermined suitably in accordance with the thermosetting resincomposition and the thermosetting resin in the conductor 29 in use, andin general, the temperature is in a range of 140 to 230° C. and thepressure is 0.3 in a range of to 5 MPa.

Next, as shown in FIG. 4E, the low-elastic material 22 is injected fromthe through holes 24 into the element-containing portion 15 by using aninjector 23. Later, as shown in FIG. 4F, the low-elastic material 22 iscured, and thus a semiconductor device according to Embodiment 2 isobtained.

For the injector 23, for example, a dispenser can be used. In analternative method, the injector 23 is not used, but a semiconductordevice in a state as shown in FIG. 4D is dipped in the low-elasticmaterial 22, and subjected repeatedly to reduction-application ofpressure so as to fill the low-elastic material 22.

Though the low-elastic material 22 can be identical to that as describedin Embodiment 1, preferably it is a liquid at the time of injection asshown in FIG. 4E and is solidified after a curing as shown in FIG. 4F.For curing, an ordinary thermosetting method can be used.

According to the present embodiment, since the cavity in theelement-containing portion 15 is filled with the low-elastic material22, deformation caused by presence of a cavity can be prevented, andthus, a semiconductor device having an excellent mounting reliabilitycan be provided.

EMBODIMENT 3

FIG. 5 is a cross-sectional view showing a semiconductor deviceaccording to Embodiment 3 of the present invention. As shown in FIG. 5,in a semiconductor device according to Embodiment 3, four circuit boards12 are laminated. Through holes 24 are formed in all of the substrates10 and provided with penetration conductors 25. Furthermore, on each ofthe bottom substrate 10 and a substrate 10 second from the bottom, asemiconductor element 11 to be contained in the element-containingportion 15 is mounted. The pair of semiconductor elements 11 arecontained facing each other in the element-containing portion 15. Alow-elastic material 22 is filled in the cavity in theelement-containing portion 15 including space between surfaces 11 a, 11a of the semiconductor elements 11, 11. Excepting these characteristics,the semiconductor device is similar to the above-mentioned semiconductordevice (see FIG. 3) according to Embodiment 2. Therefore, thesemiconductor device according to Embodiment 3 can provide effects asthose of the semiconductor device according to Embodiment 2.

Since the pair of semiconductor elements 11, 11 are contained facingeach other in an element-containing portion 15 in the semiconductordevice according to Embodiment 3, the surface area of the semiconductordevice can be reduced easily.

Next, a method for producing a semiconductor device according toEmbodiment 3 will be described below. FIGS. 6A and 6B arecross-sectional views showing process steps for a method for producing asemiconductor device according to Embodiment 3.

A plurality of circuit boards 12 are prepared in a method similar to themethod as shown in FIGS. 4A, 4B, and a plurality of sheet members 13containing a conductor 29 are prepared in a method similar to the methodas shown in FIGS. 2C to 2F. The thus obtained circuit boards 12 and thesheet members 13 are laminated alternately as shown in FIG. 6A.

Next, as shown in FIG. 6B, these components are arranged in a mold 30for clamping. The mold 30 has inlets 30 a and outlets 30 b at positionscorresponding to the through holes 24 of the circuit boards 12. The mold30 is heated under pressure, and at the same time, a low-elasticmaterial 22 is injected from the inlets 30 a so as to cure athermosetting resin composition of the sheet members 13 and thelow-elastic material 22 simultaneously for integration, and also toconnect the circuit boards 12 electrically to each other, and thereby asemiconductor device according to Embodiment 3 was obtained.

When injecting the low-elastic material 22 from the inlets 30 a of themold 30, the pressure in the mold 30 is reduced preferably by suctionfrom the outlets 30 b.

According to the producing method, since the thermosetting resincomposition can be cured and the low-elastic material 22 can be filledand cured in a process step, a semiconductor device of the presentinvention can be obtained in a simple method.

EMBODIMENT 4

FIG. 7 is a cross-sectional view showing a semiconductor deviceaccording to Embodiment 4 of the present invention. As shown in FIG. 7,in a semiconductor device according to Embodiment 4, at least onesemiconductor element 11 is mounted on each of a pair of opposingsubstrates 10. Since a plurality of semiconductor elements 11 can becontained in an element-containing portion 15 in the semiconductordevice according to Embodiment 4, the thickness of the semiconductordevice can be decreased. When plural semiconductor elements 11 varied insize are contained, surface areas of the substrates 10 can be usedefficiently, which serves to decrease the dead space that will not alloweither formation of a via-conductor 14 or mounting of the semiconductorelement 11.

The semiconductor device according to Embodiment 4 can be produced bythe method as shown in FIGS. 4A-4F.

EMBODIMENT 5

FIG. 8 is a cross-sectional view showing a semiconductor deviceaccording to Embodiment 5 of the present invention. As shown in FIG. 8,in a semiconductor device according to Embodiment 5, a low-elasticmaterial 22 is filled only in the space between upper surfaces 11 a ofsemiconductor elements 11 and substrates 10.

Next, a method for producing the above-mentioned semiconductor deviceaccording to Embodiment 5 will be described. FIGS. 9A-9D arecross-sectional views showing process steps in a method for producingthe semiconductor device according to Embodiment 5.

As shown in FIG. 9A, a low-elastic material 22 is solidified and shapedinto a sheet. For solidifying the low-elastic material 22,thermosetting, photo-curing, curing through a moisture-absorbing actionand the like can be used. The method of shaping the low-elastic material22 into a sheet is not limited particularly, and a method similar to theabove-mentioned method for shaping the sheet member 13 can be used.

Next, as shown in FIG. 9B, the sheet-like low-elastic material 22 isbonded to an upper surface 11 a of a semiconductor element 11 that isflip-chip mounted on a substrate 10, thereby a semiconductor package 26is manufactured.

Next, as shown in FIG. 9C, a plurality of semiconductor packages 26 anda plurality of sheet members 13 formed in a method similar to the methodas shown in FIGS. 2C-2F and containing a conductor 29 are laminated, andintegrated with each other by application of heat and pressure, and atthe same time, the circuit boards 12 are connected electrically to eachother with via-conductors 14, thereby a semiconductor device (FIG. 9D)according to Embodiment 5 is obtained.

According to the producing method, since the low-elastic material 22 canbe filled in the space between an upper surface 11 a of a semiconductorelement 11 and the substrate 10 without formation of any through holes,the semiconductor device of the present invention can be obtained in asimpler manner.

In the producing method, the sheet-like low-elastic material 22 isbonded to the upper surface 11 a of the semiconductor element 11.Alternatively, the low-elastic material 22 can be bonded onto thesubstrate 10 opposing the semiconductor element 11. In the step as shownin FIG. 9A, the sheet-like low-elastic material 22 is not necessarilycured as long as it can retain the shape, since the low-elastic material22 can be cured in the subsequent step of lamination-integration.

EMBODIMENT 6

FIG. 10 is a cross-sectional view showing a semiconductor deviceaccording to Embodiment 6 of the present invention. As shown in FIG. 10,in a semiconductor device according to Embodiment 6, four circuit boards12 are laminated. A semiconductor element 11 to be contained in anelement-containing portion 15 is mounted on each of the bottom substrate10 and the second bottom substrate 10 in FIG. 10. The pair ofsemiconductor elements 11,11 are contained facing each other in theelement-containing portion 15. A low-elastic material 22 is filled inthe space between the semiconductor elements 11,11. A semiconductorelement 11 to be contained in an element-containing portion 15 ismounted on each of the top substrate 10 and the second top substrate 10in FIG. 10, and a low-elastic material 22 is filled in the space betweenthe semiconductor element 11 and the substrate 10 opposing the uppersurface of the semiconductor element 11. Even when thin substrates 10 orthin semiconductor elements 11 are used in the semiconductor deviceaccording to Embodiment 6, the low-elastic material 22 suppresseswarping and deformation, and thus the mounting reliability is improved.Moreover, since the pair of semiconductor elements 11, 11 are containedfacing each other in the element-containing portion 15, the surface areaof the semiconductor device can be reduced easily.

The semiconductor device according to Embodiment 6 can be manufacturedby a method as explained by referring to FIGS. 9A-9D.

EMBODIMENT 7

FIG. 11 is a cross-sectional view showing a semiconductor deviceaccording to Embodiment 7 of the present invention. As shown in FIG. 11,in a semiconductor device according to Embodiment 7, a plurality ofsemiconductor elements 11 facing each other are flip-chip mounted oneach of a pair of opposing substrates 10, and a low-elastic material 22is filled in the space between upper surfaces of the semiconductorelements 11. Furthermore, a plurality of semiconductor elements 11 aremounted on a surface of a top substrate 10. The semiconductor deviceaccording to Embodiment 7 can provide effects similar to those of thesemiconductor device according to Embodiment 6. In addition to that,when semiconductor elements 11 varied in size are mounted, it ispossible to decrease the dead space that does not allow either formationof a via-conductor 14 or mounting of a semiconductor element 11. Thesemiconductor device according to Embodiment 7 can be manufactured by amethod similar to the method as explained by referring to FIGS. 9A-9D.

EMBODIMENT 8

FIG. 12 is a cross-sectional view showing a semiconductor deviceaccording to Embodiment 8 of the present invention. As shown in FIG. 12,a semiconductor device according to Embodiment 8 is the same as thesemiconductor device (see FIG. 3) according to Embodiment 2, except thatneither through holes 24 nor penetration conductor 25 are formed.Similar to the semiconductor device of Embodiment 2, the cavity in theelement-containing portion 15 of the semiconductor device in Embodiment8 is filled with the low-elastic material 22, and thus deformationcaused by the cavities can be prevented, and a semiconductor device withexcellent mounting reliability can be provided.

Next, a method for producing the above-mentioned semiconductor deviceaccording to Embodiment 8 will be described. FIGS. 13A-13D arecross-sectional views showing process steps in a method for producingthe above-mentioned semiconductor device according to Embodiment 8.

First, a circuit board 12 prepared by mounting a semiconductor element11 on a substrate 10, and a sheet member 13 containing a conductor 29,are laid as shown in FIG. 13A. Next, as shown in FIG. 13B, a low-elasticmaterial 22 is injected into an element-containing portion 15 formed inthe sheet member 13, thereby manufacturing a semiconductor package 26.Next, as shown in FIG. 13C, a plurality of semiconductor packages 26 arelaminated and further a circuit board 12 is laminated on the top. Thesecomponents are integrated with each other by application of heat andpressure, and at the same time, the circuit boards 12 are connectedelectrically to each other with via-conductors 14, and further thelow-elastic material 22 is cured. Thereby a semiconductor device (FIG.13D) according to Embodiment 8 is obtained.

In the producing method, after a step as shown in FIG. 13B, thelow-elastic material 22 can be cured or softly cured in order to improvethe workability of the semiconductor packages 26. In such a case, thelow-elastic material 22 must be cured or softly cured under a conditionthat avoids curing of the thermosetting resin composition of the sheetmembers 13. Examples of the methods include a method of heat-processingat a temperature lower than the curing temperature of the thermosettingresin composition, a method of photo-curing, and a method of curing bymoisture absorption.

It is preferable in the above-mentioned producing method that evacuationis carried out after the step of FIG. 13B so as to remove air bubblescontained in the low-elastic material 22.

According to the producing method, since it is possible to fill thelow-elastic material 22 without forming a through hole, a semiconductordevice of the present invention can be obtained in a simpler producingmethod.

EMBODIMENT 9

FIG. 14 is a cross-sectional view showing a semiconductor deviceaccording to Embodiment 9 of the present invention. The semiconductordevice according to Embodiment 9 is a modification of the semiconductordevice (see FIG. 12) according to Embodiment 8. As shown in FIG. 14, ina semiconductor device according to Embodiment 9, four circuit boards 12are laminated. A semiconductor element 11 to be contained in anelement-containing portion 15 is mounted on each of the bottom substrate10 and the second bottom substrate 10 in FIG. 14. The pair ofsemiconductor elements 11,11 are contained facing each other in theelement-containing portion 15. The semiconductor device according toEmbodiment 9 can be manufactured by the same method as the methodexplained by referring to FIGS. 13A-13D.

EMBODIMENT 10

FIG. 15 is a cross-sectional view showing a semiconductor deviceaccording to Embodiment 10 of the present invention. The semiconductordevice according to Embodiment 10 is a modification of the semiconductordevice (see FIG. 8) according to Embodiment 5. As shown in FIG. 15, in asemiconductor device according to Embodiment 10, through holes 24 areformed in the top substrate 10 and the intermediate substrate 10 in FIG.15. The semiconductor device according to Embodiment 10 can bemanufactured by the same method as the method explained by referring toFIGS. 4A-4F.

EXAMPLES

Examples of the present invention will be described below. The presentinvention will not be limited to the following examples.

(Mounting Reliability)

In Example 1, the above-mentioned semiconductor device (see FIG. 3)according to Embodiment 2 was manufactured by a method as shown in FIGS.4A-4F. The materials used in Example 1 and details of the manufacturingmethod will be explained below with a reference to FIGS. 4A-4F.

For each of the substrates 10, a glass-epoxy substrate 0.07 mm thick wasused. Through holes 24 (diameter: 300 μm) were formed in the vicinity ofthe element-mounting part in the substrate 10, and the through holes 24were plated to form penetration conductors 25. Semiconductor elements 11in use were silicon semiconductor elements for a connection test, eachbeing 6 mm×6 mm and 100 μm in thickness and electrodes are formed at 120μm pitch on the periphery. A gold wire 25 μm in diameter was joined ontothe electrodes of this semiconductor element 11 by using ultrasonic,thereby forming a bump. In formation of the bump, a bump bonder (STB-2by Matsushita Electric Industrial Co., Ltd.) was used.

For an underfill 19, an epoxy resin sheet (produced by Sony Chemical) 50μm in thickness and containing a silica filler was prepared. This wascut to a size substantially the same as the semiconductor element 11,and temporarily bonded onto the substrate 10 as shown in FIG. 4A.Subsequently, electrodes of the semiconductor element 11 and electrodeson the substrate 10 were positioned each other, and the semiconductorelement 11 was mounted on the substrate 10, applied with a pressure of 3MPa under an atmosphere of 200° C. so as to cure the underfill 19, andthus the circuit board 12 as shown in FIG. 4B was manufactured.

A solid prepared by blending 80 mass % of a melt silica powder and 20mass % of epoxy resin (containing a curing agent) and methyethylketone.(MEK) as a solvent were kneaded in a planetary mixer. The mixture ratioof the solid to the solvent (mass ratio) was 10:1. This mixture wasapplied onto a carrier film of polyethylene terephthalate by adoctor-blade method. Later, the MEK was evaporated to manufacture asheet member 13 (thickness: 100 μm).

This sheet member 13 was processed with a punching machine (produced byUHT) so as to form an element-containing portion 15 and through holes 28(see FIG. 2E). Then, a conductive paste was manufactured by kneading 87mass % of a silver-coated copper powder and 13 mass % of epoxy resin(containing a curing agent) by using a three-roll mixer. This conductivepaste was filled in the through holes 28 by a printing method, andthereby a sheet member 13 containing the conductor 29 (conductive paste)as shown in FIG. 4C was manufactured.

Next, as shown in FIG. 4C, three circuit boards 12 and two sheet members13 were laminated alternately and applied with heat and pressure in amold for 15 minutes under a condition of temperature: 200° C. andpressure: 2 MPa. At the same time, the conductor 29 (conductive paste)was cured to form via-conductors 14 so as to connect electrically thecircuit boards 12 (FIG. 4D).

Next, a silicone resin (TSE3051 produced by Toshiba GE silicone) as alow-elastic material 22 was injected from the through holes 24 into theelement-containing portion 15 as shown in FIG. 4E. For the injector 23,a dispenser (a production of Musashi Engineering) was used. Later,evacuation was carried out in a vacuum dryer so as to remove air bubblesremaining in the low-elastic material 22, and further a heat treatmentwas carried out for two hours at 140° C. so as to cure the low-elasticmaterial 22. Thereby a semiconductor device of Example 1 as shown inFIG. 4F was manufactured. The semiconductor device was 0.85 mm inthickness.

For a comparative example, a semiconductor device was manufactured bythe same method as in the above-mentioned Example 1 except that thelow-elastic material 22 to be injected into the element-containingportion 15 was replaced with a thermosetting resin composition forcomposing the sheet member 13.

For examining the mounting reliability of the two kinds of semiconductordevices, respectively 10 semiconductor devices were placed for 168 hoursin a thermo-hygrostat vessel of 85° C., 60% RH(RH denotes relativehumidity), which were then subjected to a reflow at a peak temperatureof 250° C. so as to measure resistance values at semiconductorconnecting portions. The results show that no conduction failureoccurred in any of the ten semiconductor devices of Example 1, while sixof ten samples experienced conduction failures of the semiconductordevices of the comparative example.

The thermosetting resin composition of the sheet member 13 and thelow-elastic material 22 (silicone resin) were heated respectively at200° C. in a flat press so as to shape into plates, and the elasticmoduli were measured by using a dynamic viscoelasticity measuringinstrument (DMS210 produced by Seiko Instrument). The results show thatat 25° C. an elastic modulus of the thermosetting resin composition was8 GPa, while an elastic modulus of the low-elastic material 22 was 50GPa.

The result shows that the mounting reliability of a semiconductor deviceis improved by filling a low-elastic material 22 whose elastic modulusis lower than the elastic modulus of the thermosetting resin compositioncomposing the sheet member 13 in the space between the semiconductorelement 11 and the substrate 10 opposing the upper surface of thesemiconductor element 11

(Heat Dissipation)

A semiconductor element 11 was mounted on a substrate 10 in the samemanner as explained in Example 1. A semiconductor element 11 to bemounted on the intermediate substrate 10 had a built-in 200 Ω resistor.Furthermore, a thermocouple was bonded onto the upper surfaces of thesemiconductor elements 11 and electrodes of the thermocouple were takenout from the through holes 24. In this state, the respective layers werelaminated in the same manner as in Example 1 so as to manufacture asemiconductor device of Example 2. A semiconductor device according toExample 3 was produced in the same manner as Example 2 except that thelow-elastic material 22 was prepared by adding to a silicone resin(TSE3051 produced by Toshiba GE silicone) 40 mass % of an alumina powder(average particle diameter: 12 μm) as a thermo-conductive filler.

The semiconductor devices of Examples 2 and 3 were subjected to electricpower of 2 W for 10 minutes, and then the temperature at the upper partsof the built-in semiconductor elements 11 in each of the semiconductordevices was measured by using the thermocouple bonded to thesemiconductor elements 11. The result shows that the temperature of thesemiconductor device in Example 2 was 82° C., and the temperature of thesemiconductor device in Example 3 was 73° C. The result shows that heatdissipation is improved when a thermo-conductive filler is added to thelow-elastic material 22, and this will improve the effect of suppressingthe temperature rise in the semiconductor elements 11.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not limiting. The scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

1. A semiconductor device having a plurality of circuit boardscomprising substrates and semiconductor elements mounted on thesubstrates, the circuit boards being bonded to each other through sheetmembers of a thermosetting resin composition, wherein the plural circuitboards are connected electrically to each other by via-conductorspenetrating the sheet members, the semiconductor elements arrangedbetween the substrates are contained in element-containing portionsformed in the sheet members, and a low-elastic material whose elasticmodulus is lower than the elastic modulus of the thermosetting resincomposition is filled in a space between semiconductor elementscontained in the element-containing portions and the substrates opposingsurfaces opposite to the mounting surfaces of the semiconductorelements.
 2. The semiconductor device according to claim 1, wherein thesemiconductor elements in the element-containing portions are sealedwith the low-elastic material.
 3. The semiconductor device according toclaim 1, wherein cavities in the element-containing portions are filledwith the low-elastic material.
 4. The semiconductor device according toclaim 1, wherein at least one of the semiconductor elements to becontained in one of the element-containing portions is mounted on eachof the two substrates covering the element-containing portion.
 5. Thesemiconductor device according to claim 1, wherein at least one of thesemiconductor elements is flip-chip mounted on the substrate.
 6. Thesemiconductor device according to claim 1, wherein the low-elasticmaterial contains a moisture-absorbing filler.
 7. The semiconductordevice according to claim 1, wherein the low-elastic material contains athermo-conductive filler.
 8. The semiconductor device according to claim1, wherein the low-elastic material has an elastic modulus of 1 MPa to1000 MPa at 25° C.
 9. The semiconductor device according to claim 1,wherein through holes are formed in the vicinity of an area of thesubstrate for mounting the semiconductor elements, and the through holescommunicate with the element-containing portions.
 10. The semiconductordevice according to claim 9, wherein penetration conductors forelectrically connecting wirings formed on both surfaces of the substrateare formed on the inner surfaces of the through holes.
 11. Thesemiconductor device according to claim 1, wherein the semiconductorelements are flip-chip mounted on a surface of a bottom substrate at theelement-containing portion side, the semiconductor device furthercomprises an external-connection electrode formed on a surface of thesubstrate opposite to the element-containing portion side, and the othersemiconductor element is mounted on the other substrate by wire-bonding.12. The semiconductor device according to claim 1, wherein thethermosetting resin composition contains inorganic filler in an mount of70 mass % to 95 mass %.
 13. The semiconductor device according to claim1, wherein the thermosetting resin composition contains a reinforcer inan amount of 15 mass % to 50 mass %.
 14. A semiconductor device having aplurality of circuit boards comprising substrates and semiconductorelements mounted on the substrates, the circuit boards being bonded toeach other through sheet members of a thermosetting resin composition,wherein the plural circuit boards are connected electrically to eachother by via-conductors penetrating the sheet members, the semiconductorelements arranged between the substrates are contained inelement-containing portions formed on the sheet members, at least one ofthe semiconductor elements to be contained in one of theelement-containing portions is mounted on each of the two substratescovering the element-containing portion, at least one pair of thesemiconductor elements are contained facing each other in theelement-containing portion, and a low-elastic material whose elasticmodulus is lower than the elastic modulus of the thermosetting resincomposition is filled in the space between the surfaces of the pair ofthe semiconductor elements.
 15. The semiconductor device according toclaim 14, wherein a cavity in the element-containing portion is filledwith the low elastic modulus material.
 16. The semiconductor deviceaccording to claim 14, wherein the low-elastic material contains amoisture-absorbing filler.
 17. The semiconductor device according toclaim 14, wherein the low-elastic material contains a thermo-conductivefiller.
 18. The semiconductor device according to claim 14, wherein thelow-elastic material has an elastic modulus of 1 MPa to 1000 MPa at 25°C.
 19. A method for producing a semiconductor device, the methodcomprising: mounting semiconductor elements on substrates so as to formcircuit boards, forming, on sheet members comprising an uncuredthermosetting resin composition, element-containing portions forcontaining the semiconductor elements and through holes to be filledwith a conductor, filling the through holes with a conductor,positioning and laminating the circuit boards and the sheet membersalternately, and subsequently applying heat and pressure while injectinga low-elastic material into the element-containing portions, where theelastic modulus of the low-elastic material is lower than the elasticmodulus of the thermosetting resin composition, so that thethermosetting resin composition and the low-elastic material are curedsimultaneously and integrated, and the plural circuit boards areconnected electrically.
 20. The method for producing a semiconductordevice according to claim 19, wherein the method further comprising:forming through holes in the circuit boards in the vicinity of areas formounting the semiconductor elements before laminating the circuit boardsand the sheet members, and injecting the low-elastic material into theelement-containing portions from the through holes.